System employing manually deactivated heating element



Jan. 15, 1963 n. E. CLAPP ETAL 3, ,9

SYSTEM EMPLOYING MANUALLY DEACTIVATED HEATING ELEMENT Original FiledApril 30, 1959 2 Sheets-Sheet 1 96 r m 5 -I\&\\\\\\\\\\\\\\\\\\\\\\\\\Mm,

r DANIEL E. CLAPP 3/ l 99 JOHN L. EATON,JR.

ATTYS- Jan. 15, 1963 D. E. CLAPP ET AL SYSTEM EMPLOYING MANUALLYDEACTIVATED HEATING ELEMENT Original Filed April 50, 1959 2 Sheets-Sheet2 FEB.

2INVEN'I'ORSI DANIEL E. CLAPP JOHN L. EATON JR.

ATTYS atent @fiice Patented Jan. 15, 1963 3,073,917 SYSTEM EMPLOYINGMANUALLY DEAGIZTI- VATED HEATING ELEMENT Daniel E. Clapp, Somerton,Philadelphia, and John L.

Eaton, Jr., Levittown, Pa., assignors to The Proctor- Silex Corporation,a corporation oi Pennsylvania Original application Apr. 30, fl95 Ser.No. 81%,952. Divided and this application Dec. 21, 1959, Ser. No.861,095

Claims. (til. zen-4) This is a division of our earlier filed pendingapplication, Serial No. 810,082, filed April 30, 1959.

This invention relates to a heating system employing a pair ofelectrical heating elements which are connected in parallel, and one ofwhich may be disconnected from the circuit in the event that reducedenergization is desired. It also relates to particular arrangements ofswitch controls useful in such a system. The invention will findparticular use in surface heating units for electric ranges.

Many electric ranges provide two coils or heating elements for eachsurface unit. Such units usually provide separate control settings forsingle and two coil energization. Typically, however, the single coil isused for low temperatures and both coils for higher temperatures.Control of temperature is achieved through a control switch or wattagecontroller which cycles open and closed,

the higher the temperature the greater the ratio of on to .ofi time fora given heater.

In designing heating elements and controls, particularly the surfaceunits of household electric ranges, it has been customary to providesufficient capacity to adequately and rapidly heat the heaviestconceivable thermal loads. Pan controls are frequently relied upon tobring the temperature of the load into correspondence with the settingof the controls. With many systems, however, it is possible for verylight loads to be overheated and burned before the feedback of controlinformation from the pan control has been eifective, and regulation oftemperature is often only approximate for most loads.

The present invention is intended to give more flexibility to a two coilsystem by permitting the use of one or both heater elements over theentire range of temperature settings. This has at least two importantadvantages. One is the ability to provide less heat per unit of on timeto achieve a given temperature in a light load, as for example, a lightcream sauce in a light pan. With less heat output per unit of time whencurrent actually passes through the heating element, the opportunity forthermal inertia to produce overshooting in the temperature of a lightload is minimized. In our system, it is possible to select a conditionof less heat output per unit of on time regardless of what cookingtemperature is desired. The second advantage is to permit more exactcontrol of temperature of heavier loads. This is true because theheating etfects are proportional to the ratio of on to oil time,corresponding to the ratio of time the control switch is closed to thetime it is open. By using one coil where two could well be used, thesingle coil will have to be energized enough more than the two to makeup for the effect of the two. This means that any fixed error in timingdue to the control defects and the like will be reduced because it willbe a smaller part of the total time the unit is on. Hence, thetemperature will be controlled more precisely.

In the system of the present invention there is provided a switchcontrol unit which has a single setting for each temperature whetheroperating with one or two heating elements. In fact, the arrangement issuch that every time the heating system is turned off, the units areautomatically reconnected in parallel. If single coil operation isdesired, it can be achieved manually after temperature selection is madeby movement of a manual actuator, which is preferably a push button. Itis even possible, and preferred, to combine the actuator with thecontrol knob so that the knob itself provides the push button.

In accordance with the present invention, a heating system comprising apair of heating elements connected in parallel is employed. A firstswitch element is placed in series with one of the heating elements anda second switch element is placed in series with the parallel circuitformed by these heating elements. The series circuit is adapted to beconnected across a power line. An actuator means is provided for thefirst switch including a latch which cooperates with the first switch sothat that switch is normally closed in series with one heater element.Release and relatching means are provided for releasing and relatchingthe latch in order to permit the first switch to assume its respectiveopen and closed conditions which correspond to diiferent latchconditions in different embodiments. A second actuator is provided tocontrol the second switch. The second actuator is also effective uponthe latch so that when the actuator moves the second switch to offposition, it also afiects the latch in such a way that the first switchis closed.

Various specific arrangements have been devised for accomplishing theseresults. Two specific embodiments of the switch arrangement are shown inthe accompanying drawings, in which FIG. 1 is a perspective view of aswitch control unit of the present invention;

FIG. 2 is a plan view of the switch control unit of FIG. 1 with thecover removed and with the main cam element withdrawn therefrom;

FIG. 3 is a sectional view along line 3-3 of FIG. 2 but taken as thoughthe switch control unit were fully assembled as in FIG. 1, and showingthe latch of the present invention in latched position;

FIG. 4 is a partial view similar to FIG. 3 but showing the latch inunlatched position;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 2 but as thoughthe switch control unit were fully assembled as in FIG. 1, showing onlypart of the cam structure, however;

FIG. 6 is a similar sectional view taken along line 66 of FIG. 2;

FIG. 7 is a plan view of the rear of the switch control unit of FIG. 1together with a schematic diagram of wiring connections to the unit;

FIG. 8 is a schematic wiring diagram of the system of the presentinvention including the system of FIGS. 1 to 7 in oli condition;

FIG. 9 is a schematic wiring diagram similar to FIG. 8 but showing onlythe critical part of the system in run condition with both heaterelements operating;

FIG. 10 is similar to FIG. 9 but showing one of the heater elementsdisconnected;

FIG. 11 is a detailed view showing the latch region in a modified formof switch control unit;

FIG. 12 is a view taken along line 1212 of FIG. 11 showing the latchsystem of FIG. 11 when the unit is in oil condition; and

FIG. 13 is a view similar to FIG. 12 in which the latch actuator and thecontacts of the switch in series with the second switch of the heaterelement are open.

Referring first to FIGS. 1 to 7, there is shown a preferred switchcontrol unit in accordance with the present invention. The control unitof FIGS. 1 to 6 is connected in a heating system as shown in FIG. 7, theoperation of which will be clear by reference to the schematic circuitdiagrams of FIGS. 8, 9 and 10. Although the primary novelty of ourinvention lies in the control unit, it will be clear that the controlunit has no utility without other circuit elements.

Referring to FIG. 'l,'ih "particular, it will be seen that the controlunit is housed Tn large part within a box molded from resinous materialand provided with appendages and other "formatidns adapted to provideadvantageous support for the structure within the box as well asappropriate openings for ventilation and access purposes. Closing thetop of the box is cover-plate 11 which also provides a bearing for ashaft upon which control 'knob 12 is mounted. Control knob 12 is provided with a calibrated dial 13 which, in operation, will be used inconjunction with 'a'r'eference mark, as for example, on the range wallwhere itis'mounted.

Within'the box are provided three major single pole, single throwswitches generally designated 14, and 16. Switch 14 functions to removeone of a pair of parallel heating units from the circuit. Switch 15 is aseries switch acting upon both heating elements which provides an on-ofiswitch. Switch 16 is a complex switch advantageously affected by meanssensing the temperature of athermal load as it is heated to cyclicallyopen and close in series with the heating elements to control thetemperature of the thermal load. All of these switches are alfect'ed insome way by the "cam mernber generally designated lfi'which'pro'videsseparate cams in the form of concentric tracks which act upon theswitches in some fashion. The cam 18 is attached to knob 12 by shaft 20to rotate with it.

As can be seen in FIGS. 2 and 3, the switch 14 is associated with alatch arrangement, generally designated 17, which determines whether theswitch is open or closed. The latch is associated with cam track 19 ofthe rotatable cam member 18. The cam track in this embodiment of ourinvention actuates the latch to latched position when the cam is rotatedto turn the system ofi. Off constitutes one rotationalposition, and itmay be only when the cam is immediately proximate cam track may beuniform in level except in the off region shown where a depression inthe track permits switch 15 to open. Track 21 preferably has only oneoff'position, the position shown, in its 360 of rotation. Thus cam 18directly determines whether and in what positionsswitch 15 is open. 7

The switch 16, as seen in FIG. 6, is actuated by still another cam track22 of cam 18, shown here in olf position. This cam track functions toposition one of the contacts of switch 16 in different positions inorder to effectively change the temperature demanded.

The structures of FIGS. 1 to 6 will be better understood following adiscussion of the switches in the entire system, as shown'schernaticallyin FIGS. '8-10, is first considered. In FIG.'8, the dashed enclosure 10corresponds to the switch control unit of FIG. 1. Within the unit areswitches 14, 15 and 16 and their associated actuators. For the mostpart, the true physical form of the actuators is not shown, but allvital parts have been representedschematically for the sake of clarity.The complete system includes first and second'heater elements '25 and'26, respectively, which may be surface pan heating coils for' anelectric range. A so-called transmitter element, within a 'dashedenclosure 27, is physically located in the proximity of the heatingelements 25 and 26 for sensing actual heat and temperature effectsresulting fromenergization of these heating elements. The

transmitter is cou'pled to switch 16 by means which may be hydraulic ormechanical as well as the electrical system shown.

FIG. 8 shows the system in o or deenergized condition wherein neithenofthe heater elements 25 or 26 is energized. FIG. 9 shows switch 15 closedso that both heater elements are connected into the circuit.

4 FIG. 10 shows switch 15 closed but switch 14 open so that the heaterelement 25 is disconnected from the circuit and deenergized. The meansof accomplishing these changes will be consideredlater in connectionwith FIGS. 1 to 6.

Referring to FIGS. 7 and 8, it can be seen that the contacts of switch14 are'electrically connected in series with heater element 25 throughterminal 3%. Heater ele ment 26 is connected inparallel with heaterelement 25 and switch 14 across terminals Bland 32. The on-oif switch 15is connected through terminal 31 in series with the parallel circuitincluding both heater elements 25 and 26. Temperature selection switch16 is connected in series with switch 15 and the parallel circuitincluding heater elements 25 and 26 through terminal 32. One of thecontacts of switch 15 is connected to line L1 of the power line throughterminal 33, and one of the contacts of switch 16 is connected throughterminal 34 to line L2 of the power line. The voltage supplied acrosslines L1 and L2 is preferably 220 volts.

In preferred embodiments of our present invention switch 16 is aso-called infinite switch. Switch 16 has one of its contacts 36selectively fixed in position corre sponding to the temperature desiredby cam track 22 actingon a cam follower'portio'n of the switch contactsupport element 37. The other switch contact 38 is preferably supportedon an element including thermomotive bimetal member 39 relative to whichis positioned a heating element 40 which is connected eifectively toline L1 through on-oflf switch '15 by way of terminal 45. Heater"element 40, in turn, is connected from terminal '31 through a lowvoltagepilot circuit to the transmitter 27. Specifically it is connected inseries with a switch 41 which is cyclically opened and closed inresponse to a thermomotive actuator 42 which responds in part to thetemperature sensed from a temperature sensing element 43 and in part tothe heat from heater element 44. Heater element 44 is in series with thecontacts of switch 41 and heater element 49, and is connected to lowvoltage line N to supply a pilot voltage, prefereably of volts, to thispilot circuit.

In operation the temperature of a pan will cause the bimetal to heat bythermal conduction. Additionally the bimetal of the sensor element 43 isheated by heater 4-4. Eventually this combined heating will cause switch41 which is mechanically coupled to the bimetal to open and stop currentflow in heater 44 as well as in heater 40. As its bimetal coolsslightly, sensor 43 will permit switch 41 to close. Meantime, thecooling of heater element 40 will have caused bimetal 31 to open thecontacts 36-38 of switch 16 by moving contact 38. Upon restoring thecurrent flow through heater element 49 these contacts of switch 16 willagain close. The position of contact 36 will determine how soon theswitch will open and close and hence is used to pro-select temperature.Since the system takes into account the heating effect actuallyresulting from the operation of heating elements 25 and 26, a highlyaccurate control of temperature and heating results.

As can be seen in FIG. 7, the terminal connection of box 112 betweenheater element and switch contact 41 is terminal 45. Also connected tothe neutral line end is low wattage pilot lamp 46 which in turn isconnected through terminal 47 to a contact 48 which is adapted to makecontact with a portion of switch 15 when the switch is closed, therebycausing lamp 46 to be lit when the system is in operation but to beextinguished when the system is not operating (i.e., when it is off).

When the contacts 50 and 51 of switch 15 are open no current will flowthrough the system. When contacts 5% and 51 are closed, as in FIG. 9,provided contacts 52 and 53 of switch 16 are also closed, current flowsthrough both heating elements 25 and 26. Contacts 52 and 53 are heldclosed by latch 17 when latch prop 54 engages the rotatable member 56.When the latch prop 54 is released by actuator 55, however, as shown inFIG. 10, the rotatable latch member 56 is free to rotate, and due to thenatural resilience of the support 57 of switch contact 53 the switch isurged open as shown in FIG. wherein contacts 52 and 53 are separated. Inthis condition current cannot flow through heater element 25 so thatelement 26 supplies all the heating. Obviously much less heat isproduced per unit of time while current is flowing, but a predeterminedtemperature is maintained through the feedback from transmitter 27 toswitch 26. This may necessitate an increase in the ratio of open toclosed time for switch 16, but this will be accomplished automaticallyby this thermal servo system.

To obtain the advantage of the operation described in connection withthe circuit shown in FIGS. 8 through 10, it is important to have anuncomplicated switch control unit capable of operation by anyone withoutappreciable instruction. In accordance with our present invention, theactuators for the various switches are associated with one another suchthat the cam which provides actuator means for switches and 16cooperates with the actuator means for switch 14 and specifically withthe latch 17.

Referring again to the structure shown in FIGS. 17, as previously notedthe integral box 10 provides ribs, bosses, shoulders, and other mountingsurfaces. As seen in FIG. 5, a portion of the box is made to extendbelow the general level of the bottom of the box. For example, as seenin FIG. 6, the general depth of the box is extended at the end whichaccommodates the switch element 16. For ventilating purposes in view ofheater 40, a large portion of the bottom, and even a portion of thesidewall of the box in this area, is omitted. Similarly, at the oppositeend of the box a deepened and bottomless portion has been provided. Thepurpose of this portion is of no significance in this case and hencewill not be discussed except to say that it permits terminals and otherelements to be protected by location in a recessed region outside of thebox.

From FIGS. 3 and 4 it can readily be seen that the shaft which supportstemperature selection knob 12 is adapted to pass through a bearingregion in the coverplate 11 of the box. The diameter of the portion ofshaft 20 Within the box is reduced, and this reduced diameter portion 55passes through the center of the box to an embossed region 61 on thebottom thereof which is bored to slidably engage the end of shaft 55 asa bearing. The reduced diameter portion '55 of the shaft also passesslidably through a central bore in cam 18. Cam 18 is provided with acup-like recess 62 arranged coaxially with the bore through the cam 18and into this recess a helical spring 63 is introduced around reduceddiameter shaft portion 55. Spring 63 at its opposite end from that received in recess 62 bears against a spring-like spider 64 which is fixedagainst the shoulder 65 between the reduced diameter portion 55 andshank portion 66 of shaft 20'. The center of the spider is held againstthe shoulder 65 so that it cannot rotate and its legs are fixed inrecesses in the cam. A snap ring 67, or other suitable stop, is providedto bear against the closure plate 11 to hold the shaft assembly 26 inposition within the housing against the urging of spring 63.

Cam 18, in addition to the coaxial cam tracks 19, 42 and 22, alreadydescribed, is provided with a bearing track 69 against which the tops ofposts 7t), 71 and 72 bear (see FIG. 2) to keep the cam in apredetermined orientation and axial level within the box 10. Posts 70,71 and 72 are preferably integrally cast in the box but may be providedwith metallic bearing surface caps which make the actual contact withthe cam track 69. It will be seen that the three points of contactprovide stable support of the cam assembly 18 in opposition to theaction of spider spring 64 and spring member 59 fixed to cover 11 topress against cam 18 in a track 60 in the top surface thereof. Spider 64and spring 59 also add stability as well as holding the cam down againstthe posts.

It will be observed that despite the fixed position of cam 18 the shaft20 itself is axially movable by pressing inwardly towards the box cover11 on knob 12. The change of position which results from such inwardpressure is shown in FIG. 4 wherein it can be seen that by pressure onshank 20 spider 64 is flattened and helical spring 63 is compressedsince cam member 18 is unyieldingly held by its support posts 70, 71 and72.

The movement of shank 20 has to do with the releasing of latch 17 whichis associated with switch 14. As can be seen in FIGS. 2 and 3, fixedcontact 52 of switch 14 is supported on the bottom of the switch box 10by means of a support-conductor which connects it externally to terminal31. Movable contact 53 of switch 14 is con nected by a rivet 77 throughresilient spring metal strip support 57 mechanically to a pedestal 76formed integrally on the box bottom. Rivet 77 also connects strip 57electrically and mechanically to terminal 36 external of the box. Thusterminal 30 is connected electrically through rivet 77 and strip 57 tocontact 53. The latch structure 17, which holds the contacts 52 and 53closed, acts upon strip 57 to accomplish this purpose. Preferably .thelatch consists of a generally triangular piece 56 pivotally supported bypivot 81 between walls 82 and 83 which extend upward from the bottom ofthe box and are integrally formed therewith. The rotatable member isprovided with at least one laterally extending member 84 generallyperpendicular to the plane of the rotatable member 56 and adapted tooverlie the switch contact support 57. A cam follower tab 86 onrotatable member 56 is adapted to be moved by cam track 19 in aclockwise direction, as viewed in FIG. 3. This movement tends to movespring-like contact support element 57 downward to close contacts 52 and53 in opposition to the spring effect of support 57 which normally urgesthe contact 53 away from contact 52. A portion of the latch projection87 of the rotatable latch member 56 is adapted to extend through a slotin the bottom of the box when in the position of FIG. 3 but to moveupwardly under the urging of resilient member 57 into the position shownin FIG. 4 when released. In moving clockwise from the position of FIG. 4to the position of FIG. 3, the latch prop 54, if in the position of FIG.3 due to the return of actuator shaft 20 to the position of FIG. 3, willbe urged downwardly away from the bottom of the box by the cam surface89 of projection 87. The resilience of latch prop 54 normally holds itagainst the bottom of the box to which it is fixed by a rivet 96. Whenthe projection 87 reaches the point that the latch shoulder 91 passesthe end of latch prop 54, the latch prop 54 will snap resiliently backinto position against the bottom of the box so that its end 92 bearsagainst shoulder 91 and holds the rotatable member 56 againstcounter-clockwise rotation even through the cam track 19 is changed fromthe off position of FIG. 3 to some energized position such as that shownin FIG. 4.

Referring now to FIG. 5, it will be seen that the onoff switch contacts'50 and 51 of switch 15 are controlled by cam track 21 of cam 18 througha cam follower portion 94 of spring arm 95 which is fixed to a pedestal96 on the bottom of the box by rivet 97. Spring arm 95 mechanicallysupports movable contact Stl and provides an electrical current paththrough rivet 97 to terminal 33. Fixed contact 51 is connected by meansof a common support plate 98 with fixed contact 52 of switch 14 throughinterconnecting rivet 99 to terminal 31. In addition, low voltage springcontact 48, which makes contact with support spring 95 of switch contact50 when contact 56 is closed against contact 51, is supported upon thebox and connected to terminal 47 which extends through an opening in theswitch box and is fixed to the bottom on the inside thereof.

Finally, referring to FIG. 6 and FIG. 2, it will be seen that the camtrack 22 bears against cam follower 100 on contact support assembly 37which supports contact 36 of switch 16. This contact can be repositionedfor different temperature settings but is fixed for any given settingexcept that the resilience of its support structure 37 permits someyielding under the pressure of contact 33 due to overclosure. Thesupport structure 37 is connected mechanically and electrically to plate102 which, as seen in FIGS. 2 and 3, extends laterally to-a rivet 1G3which, in turn, connects it'to its terminal 34- (see FIG. 3). Aninsulator strip 104 beneath plate 102 prevents shorting of the plateagainst the movable support structure of switches 14 and 15 over whichit passes. Contact 38 of switch 16, which opposes contact 36, issupported on a complex support structure 105 which includes heaterelement 41 (see FIG. 2) and bimetal 39. The construction of the switchpreferably makes it a snap switch to insure rapid parting of thecontacts. Support structure 165 is fixed by rivet 166 to a portion ofthe bottom of box 10' and at the same time to terminal 32.

In operation, the knob 12 is started from an off position, the conditionshown in FIG. 8 and in FIG. 3 and indicated on the dial 13 which has itszero placed opposite a calibration mark on the supporting structure ofthe range. Knob 12 is rotated-to a position wherein dial 13 indicatesthe desired temperature. As seen in FIG. 3 when in off position, thelatch structure 17 is latched, holding contacts 52 and 53 closed. As theknob 12 is rotated to some temperature selection position, the latchremains latched and the contacts 52-53 closed despite removal of theportion of cam track 19 which causes relatching, if required. In thisoperating condition, as shown in FIG. 9, with the contacts of switch 14closed the heating elements 25 and 26 will both be active. The switch 16will cycle open and closed to control the effective temperature of theload by controlling the proportion of total time current may passthrough the heating elements 25 and 26.

if it is desired 'to use a load of relatively low mass and thermalcapacity, switch 14 may be opened as shown in FIG. 10 in order thatheating element 25 beremoved from the circuit and only heating element26 be left active. This is accomplished by pressing the knob inwardly.This pressure causes compression of the spring 63 from the positionshown in FIG. 3 to theposition shown in FIG. 4 which permits the reduceddiameter portion 55 of the shaft to pass through the bottom of thehousing and into contact with latch prop 54. This movement urges thelatch prop 54 to move below the bottom of the shoulder 91 of therotatable latch member 80. Under the urging of spring '7 on lateralportion 84 the rotatable member as will move to the position shown inFIG. 4, thus moving the projection 37 out of the way of latch prop 54.To relatch the latch 17 and close the contacts of switch 14, it isnecessary to return the knob 12 to the Zero position. In the course ofthis movement cam track 19 will bear against cam follower projection 86on the rotatable latch member 56 and cause its clockwise rotation aboutpivot 81. This will urge the cam surface 89 of the projection 87 againstresilient latch prop 54 to displace it outwardly away from the bottom ofthe box until shoulder 91 on rotatable latch member as is passed. Atthis point the latch prop 54 will snap back against the bottom of boxand its end 92 will engage shoulder 91 and thus hold the rotatable latchmember position to close the contacts of switch 14. Thereafter when theknob turns the actuator to some on position both heating elements willbe energized.

Conceivably in some applications switch 16 might be omitted. Howeverthis would be rare because there would be no control of the temperaturewithout switch to. However, the switches 14 or 16 may be combined sothat only two switches are employed. The three switch arrangementdescribed is preferred to afford more flexibility in the design ofswitch 16.

It will be apparent to those skilled in the art that instead of usingthe knob asacommon means of applying force to the respective actuatorsystems it would be possible to have separate forces-applying means. Forexample, it would be possible to have concentric with knob 12 a pushbutton rigidly connected to smaller diameter portion 55 and have thelarger diameter portion as merely a sleeve through which a shaft, thediameter of reduced diameter portion 55, passes and connects 'directlyto the separate push button. Even more complete separation is possibleby having the push button located to one side of the knob. In such acase, however, the push button would be limited in its location iflinkage arrangements were not to become complicated by the fact thatthere must be coaction in the system of the present invention betweenthe latch system portion of the actuator of switch 14- and the cam meanswhich functions primarily as an actuator for switches 15 and 16.

A modified version of the present invention, and specifically the latcharrangement, is shown in FIGS. 11-13. As in the other drawings, thestructure is mounted on the bottom of the box 10 at about the centerthereof. The cam 18' has a cam track 19' which acts upon a rotatableportion of the latch element. In this case there is a fixed contact 52and a movable contact 53 which is supported by a modified support stripwhich overlies the rotatable member 80 and is supported on the bottom ofthe box It) by a suitable fastener means 111 which also provides asuitable electrical connection. Support strip 110 is resilient andnormally urges the contact 53 downwardly against contact 52. Rotatablemember 80' pivots about a fulcrum provided by the box at the junction ofrotatable member 80' and a crank member 112, extending through thebottom of the box. The crank member has one of the crank arms positionedbelow the reduced diameter portion of shaft 55' which when moved fromthe position shown in FIG. 12 to the position shown in FIG. 13 causesclockwise rotation of arm 113 on crank member 112, thereby causingclockwise rotation of an elongated rotatable latch member 80 about thefulcrum at the junction between it and crank 112 adjacent one endthereof. This clockwise-rotation causes member 80' to ear against member110 raising contact 53 away from contact 52' in opposition to resilientstrip 110. At the far end of rotatable member 80' is a latch element 114which when raised sufficiently will be forced over fixed shoulder 115formed in metallic member 116 which is affixed to and lies along onewall of the box 10. The spring effect of member 110 will cause thesemembers to remain in position, once latched, until released by the cam.Release occurs when the portion of cam track 19' shown in FIG. 12 againoverlies the cam surface of rotatable member 861' forcing the wholestructure back into the position shown in FIG. 12. FIG. 12 thusrepresents the off position of the switch corresponding to switch 15. Asthe dial is set at a particular temperature range, the cam track 19' nolonger prevents rotation of the rotatable latch member Sit. This normaloperating condition for both heating elements can be easily visualizedand has therefore not been illustrated. Thus when actuator 55' ispressed downwardly, as shown in FIG. 13, against the lever arm 113, therotatable member 8t) rotates and the latching action takes place.Latching, in this instance, opens rather than closes the switch contacts5253 and holds them open until closed once again by action of cam track19' on cam rotatable latch member 80.

The embodiments of the invention shown have not been limited in any wayas to application and the type of transmitter or feedback elementillustrated in FIG. 8 should not be taken to imply that the systemsdescribed are limited to use with surface units for electric ranges. Ourinvention may, in fact, be employed with wattage controllers of alltypes and for all purposes in which an adjustable heat capacity may bedesirable. In addition to being useful on the top of the range, theheating elements 25 and 26 may be used within an oven, for example.

When used with a heating unit for the top of an electric range, it maybe desirable in some instances to make the switch 14 normally openinstead of normally closed. This would have the effect of initiatingheating of only one of the heater elements which may be the smallerelement and would be in line with the usual practice of providing asingle smaller element for smaller pans and giving the larger capacityof the whole surface unit for larger pans. If this were done, actuationof the push-button might serve to close the switch and energize bothunits. In any event, the present invention is intended to be osufficient scope to cover the various possible combinations of eitherinitially open or closed switches with latches initially either latchedor unlatched.

Several embodiments of the present invention have been shown andmodifications have been suggested. Other modifications will occur tothose skilled in the art. All such modifications within the scope of theclaims are intended to be within the scope and spirit of the presentinvention.

We claim:

1. A switch control arrangement comprising at least first and secondswitches within a switch box, a shaft extending through the switch box,a cam rotatable with said shaft to be manually rotata'bly positioned bysaid shaft to determine closed and open positions of the second switch,means permitting axial movement of said shaft relative to said cam,spring means urging the shaft in a given axial direction, a latchengaging a biased contact-carrying blade of the first switch arranged tohold said switch in one of its conditions against the bias of saidblade, a cam track on said cam to move the latch to a given conditionand thereby move the contacts of said first switch to a given condition,operable only when said cam is rotated to a position in which saidsecond switch is open, means whereby axial movement of said shaft intosaid latch against the bias of said spring changes the latch conditionand thereby the first switch condition, and means preventing said latchfrom returning to said given condition, when said shaft is released andmoves out of engagement with said latch under the influence of saidspring, until the second switch is again opened by manual rotation ofsaid cam.

2. The structure of claim 1 in which the shaft actuating the latchpasses directly through the center of the cam and defines the axis ofrotation of the cam and spring means urging the shaft out of contactwith the latch.

3. The structure of claim 2 in which the shaft supports the cam forrotation with the shaft but is axially movable relative to the cam whichis supported against axial movement.

4. The structure of claim 3 in which the latch is comprised of arotatable latch member resiliently urged out of latching position and aresilient latch prop which engages and holds the rotatable member inposition and in which the shaft is movable against the latch prop inorder to release the rotatable latch member and in which the cam isadapted to reposition the rotatable member so that it can be reengagedby the latch prop.

5. The structure of claim 3 in which the shaft is movable into arotatable latch member resiliently urged out of latching position tocause it to move relative to a fixed latching element with which itbecomes engaged and in which the cam is adapted to release the rotatablemember from the fixed latching member.

References Cited in the file of this patent UNITED STATES PATENTS2,531,764 Binus et a1. Nov. 28, 1950 2,603,725 Dietrich July 15, 19522,666,124 Vogelsberg Jan. 12, 1954

1. A SWITCH CONTROL ARRANGEMENT COMPRISING AT LEAST FIRST AND SECONDSWITCHES WITHIN A SWITCH BOX, A SHAFT EXTENDING THROUGH THE SWITCH BOX,A CAM ROTATABLE WITH SAID SHAFT TO BE MANUALLY ROTATABLY POSITIONED BYSAID SHAFT TO DETERMINE CLOSED AND OPEN POSITIONS OF THE SECOND SWITCH,MEANS PERMITTING AXIAL MOVEMENT OF SAID SHAFT RELATIVE TO SAID CAM,SPRING MEANS URGING THE SHAFT IN A GIVEN AXIAL DIRECTION, A LATCHENGAGING A BIASED CONTACT-CARRYING BLADE OF THE FIRST SWITCH ARRANGED TOHOLD SAID SWITCH IN ONE OF ITS CONDITIONS AGAINST THE BIAS OF SAIDBLADE, A CAM TRACK ON SAID CAM TO MOVE THE LATCH TO A GIVEN CONDITIONAND THEREBY MOVE THE CONTACTS OF SAID FIRST SWITCH TO A GIVEN CONDITION,OPERABLE ONLY WHEN SAID CAM IS ROTATED TO A POSITION IN WHICH SAIDSECOND SWITCH IS OPEN, MEANS WHEREBY AXIAL MOVEMENT OF SAID SHAFT INTOSAID LATCH AGAINST THE BIAS OF SAID SPRING CHANGES THE LATCH CONDITIONAND THEREBY THE FIRST SWITCH CONDITION, AND MEANS PREVENTING SAID LATCHFROM RETURNING TO SAID GIVEN CONDITION, WHEN SAID SHAFT IS RELEASED ANDMOVES OUT OF ENGAGEMENT WITH SAID LATCH UNDER THE INFLUENCE OF SAIDSPRING, UNTIL THE SECOND SWITCH IS AGAIN OPENED BY MANUAL ROTATION OFSAID CAM.